Nicotine exhibits a variety of pharmacological effects (Pullan et al., N. Engl. J. Med. 330:811-815 (1994)), some of which are due to neurotransmitter release (See, for example, Sjak-shie et al., Brain Res. 624:295 (1993), where neuroprotective effects of nicotine are proposed). For example, acetylcholine, dopamine, norepinephrine, serotonin and glutamate are released by neurons upon administration of nicotine (Rowell et al., J. Neurochem. 43:1593 (1984); Rapier et al., J. Neurochem. 50:1123 (1988); Sandor et al., Brain Res. 567:313 (1991) and Vizi, Br. J. Pharmacol. 47:765 (1973), (Hall et al., Biochem. Pharmacol. 21:1829 (1972), (Hery et al., Arch. Int. Pharmacodyn. Ther. 296:91 (1977)), and Toth et al., Neurochem Res. 17:265 (1992)). Confirmatory reports and additional recent studies show that nicotine administration modulates glutamate, nitric oxide, GABA, takykinins, cytokines and peptides in the central nervous system (CNS) (reviewed in Brioni et al., Adv. Pharmacol. 37:153 (1997)). Nicotine also reportedly potentiates the pharmacological behavior of certain pharmaceutical compositions used to treat certain disorders. See, for example, Sanberg et al., Pharmacol. Biochem. & Behavior 46:303 (1993); Harsing et al., J. Neurochem. 59:48 (1993) and Hughes, Proceedings from Intl. Symp. Nic. S40 (1994). Various additional beneficial pharmacological effects of nicotine have been proposed. See, for example, Decina et al., Biol. Psychiatry 28:502 (1990); Wagner et al., Pharmacopsychiatry 21:301 (1988); Pomerleau et al., Addictive Behaviors 9:265 (1984); Onaivi et al., Life Sci. 54(3):193 (1994); Tripathi et al., J. Pharmacol. Exp. Ther. 221:91(1982) and Hamon, Trends in Pharmacol. Res. 15:36 (1994).
In addition to nicotine itself, a variety of nicotinic compounds are purportedly useful for treating a wide variety of conditions and disorders. See, for example, Williams et al., Drug News Perspec. 7(4):205 (1994); Arneric et al., CNS Drug Rev. 1(1):1 (1995); Arneric et al., Exp. Opin. Invest. Drugs 5(1):79 (1996); Bencherif et al., J. Pharmacol. Exp. Ther. 279:1413 (1996); Lippiello et al., J. Pharmacol. Exp. Ther. 279:1422 (1996); Damaj et al., Neuroscience (1997) J. Pharmacol. Exp. Ther. 291:390 (1999); Chiari et al., Anesthesiology 91:1447 (1999); Lavand'homme and Eisenbach, Anesthesiology 91:1455 (1999); Holladay et al., J. Med. ChemChem. 40(28):4169 (1997); Bannon et al., Science 279: 77 (1998); PCT WO 94/08992, PCT WO 96/31475, PCT WO 96/40682, and U.S. Pat. No. 5,583,140 to Bencherif et al., U.S. Pat. No. 5,597,919 to Dull et al., U.S. Pat. No. 5,604,231 to Smith et al. and U.S. Pat. No. 5,852,041 to Cosford et al.
Nicotine and various nicotinic compounds are reportedly useful for treating a wide variety of CNS disorders. See, for example, U.S. Pat. No. 5,1871,166 to Kikuchi et al., U.S. Pat. No. 5,672,601 to Cignarella, PCT WO 99/21834 and PCT WO 97/40049, UK Patent Application GB 2295387 and European Patent Application 297,858. CNS disorders are a type of neurological disorder. They can be drug-induced; attributed to genetic predisposition, infection or trauma; or of unknown etiology. CNS disorders include neuropsychiatric disorders, neurological diseases and mental illnesses, and include neurodegenerative diseases, behavioral disorders, cognitive disorders and cognitive affective disorders. There are several CNS disorders whose clinical manifestations have been attributed to CNS dysfunction (i.e., disorders resulting from inappropriate levels of neurotransmitter release, inappropriate properties of neurotransmitter receptors, and/or inappropriate interaction between neurotransmitters and neurotransmitter receptors). Several CNS disorders can be attributed to a deficiency of choline, dopamine, norepinephrine and/or serotonin.
Relatively common CNS disorders include pre-senile dementia (early-onset Alzheimer's disease), senile dementia (dementia of the Alzheimer's type), micro-infarct dementia, AIDS-related dementia, Creutzfeld-Jakob disease, Pick's disease, Parkinsonism including Parkinson's disease, progressive supranuclear palsy, Huntington's chorea, tardive dyskinesia, hyperkinesia, mania, attention deficit disorder, anxiety, dyslexia, schizophrenia, depression, obsessive-compulsive disorders and Tourette's syndrome.
Pain can be classified in various ways and can be characterized by a variety of geneses and etiologies (e.g., inflammatory pain, neuropathic pain, chronic pain). Current pain therapy is dominated by two classes of drugs, the non-steriodal anti-inflammatory drugs (NSAIDs) and the opioids, both of which have significant therapeutic liabilities. Various compounds which target nAChRs have been shown to be effective in treating one or more kinds of pain in animal models. See for instance, Damaj et al., J. Pharmacol. Exp. Ther. 291:390 (1999); Damaj et al., Neuropharmacology 39:2785-2791 (2000); Chiari et al., Anesthesiology 91:1447 (1999); Lavand'homme and Eisenbach, Anesthesiology 91:1455 (1999); Holladay et al., J. Med. Chem. 40(28):4169 (1997); Bannon et al., Science 279: 77 (1998); and Bannon et al., J Pharmacol Exp Ther. 285:787-794 (1998). It would be beneficial to provide pain relief without the gastrointestinal liabilities of the NSAIDs or the abuse potential of the opioids.
A limitation of some nicotinic compounds is that they are associated with various undesirable side effects, for example, by stimulating muscle and ganglionic receptors. It would be desirable to have compounds, compositions and methods for treating pain and preventing and/or treating various conditions or disorders (e.g., CNS disorders), including alleviating the symptoms of these disorders, where the compounds exhibitnicotinic pharmacology with a beneficial effect (e.g., upon the functioning of the CNS), but without significant associated side effects. It would further be highly desirable to provide compounds, compositions and methods that effect CNS function without significantly effecting those receptor subtypes which have the potential to induce undesirable side effects (e.g., appreciable activity at cardiovascular and skeletal muscle sites). The present invention provides such compounds, compositions and methods.